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I've used the pressure breath before at high elevations, but I was never told exactly what is happening and how the pressure breath works. Now I'm curious. Can anyone offer an explanation of what is going on in the lungs during a pressure breath (besides the obvious increased pressure)? I've searched around but didn't find much as far as an explanation. The best I found was:

Pressure breath helps to improve gas exchange across the alveoli by increasing the pressure in the lungs. The pressure breath helps to combat the effects caused by decreasing atmospheric pressure as climbers gain altitude.

From that, my best guess is that alveoli are not as efficient at the lower atmospheric pressures. By increasing the pressure in the lungs during a pressure breath you are basically making it seem like you are at a lower elevation (higher atmospheric pressure). And as a result the alveoli function better. Any thoughts?

It was explained to me via a garden hose analogy: when you put your thumb over the hose opening the pressure increases and so the water sprays out at higher pressure while, conversely, the blockage creates increased pressure inside the hose (i.e. back pressure). The same thing goes on with the pressure breath, with the result that the increased back pressure forces more oxygen into your lungs. So in effect, the higher internal pressure "crams" more oxygen into the lungs, to use non-technical language, so you are getting more efficient oxygen exchange (compared to normal breathing at altitude). That made sense to me so I never sought further explanation, though I'd be happy to be corrected by a physician or the like.

Thanks, that's a good analogy with the garden hose and back pressure.

Since the pressure breathe is only happening when you exhale, I wouldn't say you force more oxygen into your lungs (since you are stuck with whatever oxygen you got on your inhale) but rather, like you say, the pressure breath out increases the efficiency of the oxygen/CO2 exchange as the air moves out of your lungs.

Unless the pressure breath out sets you up for more efficient oxygen exchange on your next breath in. I'm not sure at what point (inhale or exhale) the improved oxygen exchange occurs.

Sorry to be pedantic, I'm just curious. I should probably just accept the fact that it works and keep on climbing

My understanding is that the pressure part of pressure breathing is bullshit. You really can't blow that hard just by pursing your lips. Even blowing into a closed tube about the best most people can manage is roughly 0.1atm. The main benefit of pressure breathing is the breathing part. You breath more. So go ahead and purse your lips and make choo-choo noises if it works for you but don't pretend it's significantly elevating the pressure in your alveoli. It's not.

Or I could be wrong.

"Pressure breathing" is also called "Auto PEEP" and "purse-lip breathing."

PEEP = Positive End-Expiratory Pressure

Auto PEEP (or whatever you want to call it) reduces the work of breathing by keeping a bit of positive pressure in the lungs at the end of expiration, just a bit over ambient pressure. This PEEP prevents the alveoli sacs from completely collapsing at the end of expiration.

The analogy is the balloon from the party store. The initial breath to get the balloon open takes a lot of pressure, but once it's blown up you can inflate and deflate rather easily - as long as you don't let the balloon fully collapse between breaths. If you let the balloon fully deflate, then it takes a hard breath to re-inflate.

Auto PEEP is like keeping the balloon slightly inflated at the end of expiration, making it easier to re-inflate with an inspiration.

Auto PEEP is a natural way to breath, and we do it automatically without anyone teaching you how to do it. Because it works. There is improved oxygenation and less work of breathing because you are keeping your alveoli open.

Have often wondered about this. I have severely compromised lungs - exercise induced asthma, then scarring from pneumonia, and then a massive bilateral pulmonary embolism following blood clots in a broken leg, where the clots in the lungs didn't fully dissolve after the hospital stay, as per a VQ scan, and the lungs are mostly dead tissue and dead air sacs behind the clots.

The harder I climb, or otherwise stress my lungs, like with a bad cold/bronchitis, the more likely I am to find myself making a sighing noise on the exhale when I sleep, and also a kind of whiny noise on the exhale toward the end of a long hard climbing day, which is almost as involuntary as when I'm asleep. This has nothing to do with being at altitude now, although I think it only used to happen (before the PE) when I was sleeping at high altitude (haven't been over 14K since). It's not sleep apnea (on the inhale) or snoring.

I've heard some guide companies make you whistle or something to force the pressure breath, and I figured my involuntary noise was the body instinctively voicing the exhale, since voicing requires more air to be expelled than just breathing. From your explanations, sounds like this process works for whatever is causing a lack of oxygen, not just high altitude? If so, seems like the involuntary nature in my case, with the body just responding to a need, lends credence to the concept?

Alveoli in a healthy lung don't completely collapse at the end of each exhalation.

Does pressure breathing make it easier for someone with healthy lungs to take a breath? Maybe. But I think the main benefit is that it is one way to focus on breathing more. Show me the study that demonstrates that pursed lip breathing provides significantly better oxygenation in healthy climbers than simply breathing deeply at the same volume rate.

JD, I tend to agree with you that "pressure breathing" just causes you to focus more on breathing (getting deeper, controlled breathes) and that would have a better overall effect on your blood O2 level.

But, after reading a bit more about Auto PEEP (thanks, Sierra), I believe there is a bit of validity to it. To what effect? I have no idea. A study would be interesting to see. But it sort of makes sense and I'll explain my interpretation of it.

Breathing normally the pressure in your lungs is equal to ambient pressure at the end of each breath. At or near sea level that is 14.7 psi. This is the pressure your lungs are accustom to working at. Now let's say you are at 10,000', which is 10.1 psi ambient pressure. If you breath normally your lungs will see 10.1 psi at the end of each breath. To combat the drop in ambient pressure, you can Auto-PEEP to increase the pressure in your lungs during each exhale. A normal person is capable of a breath pressure of 1-2 psi, so by pressure breathing you can increase your lung pressure from 10.1 psi to 11.1-12.1 psi during each exhale, closer to the 14.7 psi you are used to.

I'm kind of just talking out my ass, but that's what I gathered from the bit of reading I did. Now the question is how much of an effect that little bit of increased pressure has. My guess is not as much as having nice, controlled deep breaths (belly-breathing).

I doubt people generate 1-2 psi with each exhalation during pursed lip breathing. It's not easy to blow that hard. Try it.

From what I can gather off the web, during normal exhalation the pressure differential is less than 1 mmHg (0.02 psi). With pursed lip breathing it increases to something like 5 cmH20 (0.07 psi). That's with patients who have lung disease, not hardy mountaineers at altitude.

A typical latex party balloon inflates at 15 or 16 psi, and pops below 17. Most people can manage to inflate a balloon, and many can pop it with their breath, so 1 or 2 psi is a reasonable guess at how hard a lung can push when it's working fairly hard.

I don't think just pursing your lips is enough to raise your lung pressure a full psi (breathing through pursed lips is much easier than inflating a balloon), but maybe consciously blowing harder at the same time will get you close.

OK, googling around a bit more, it seems a good way to measure exhalation strength is to try to lift a column of water via a U-shaped manometer. Online discussions seem to converge around five feet of water (2psi) as the max for an average man, with rare individuals able to double that.

I worked in an instrument shop with a 100" H2O manometer, we had a contest. Most of the guys could get between 50" and 80" but there was one guy that could blow it out.

That's with rests between attempts, I'm assuming. Keeping it up all day long is another story.

nartreb wrote:...it seems a good way to measure exhalation strength is to try to lift a column of water via a U-shaped manometer.

That's exactly what I meant when I said "try it".

I did this several years ago when I was measuring the pressure of something with a length of vinyl tubing and got curious. I managed 2psi with difficulty. I suspect generating 1psi with each exhalation would give you a headache. It's probably dangerous to repeatedly bear down like that. Imagine blowing up balloons non-stop for hours.

Interesting, nartreb. It didn't cross my mind to think about infalting a balloon, but I think it is a good analogy.

Just to clarify your post so no one gets confused: when you mention 15 and 16 psi, you are talking about absolute pressure (psia). To get gauge pressure (the pressure you actually generate with your lungs), you subtract ambient pressure (14.7 psi for simplicity sake), which gets you 0.3 to 1.3 psig.

We can get real sciency with this. By blowing into a sealed bag via a known orifice/nozzle size (e.g. small section of tube), we can measure the (assumed constant) flow rate and in turn estimate the pressure differential across the nozzle. One side will be atmosphere (0 psig) and the other side will be the pressure generated by your lungs. By changing the orifice sizes, you can try to replicate the feeling of breathing hard through pursed lips.

I did some experiments with different kinds of breathing like this while at high altitude in the Himalayas in April and May, while sitting in camp and wearing a pulse oximeter on my finger. I could raise my blood oxygen level a percentage point or two by pressure breathing as compared to normal breathing, but I could raise it more by hyperventilating. So I suspect that concentrating on taking deeper breaths and exhaling more forcefully while climbing instead of pressure breathing may be a better strategy.

Sierra Ledge Rat wrote:"Pressure breathing" is also called "Auto PEEP" and "purse-lip breathing."

PEEP = Positive End-Expiratory Pressure

Auto PEEP (or whatever you want to call it) reduces the work of breathing by keeping a bit of positive pressure in the lungs at the end of expiration, just a bit over ambient pressure. This PEEP prevents the alveoli sacs from completely collapsing at the end of expiration.

The analogy is the balloon from the party store. The initial breath to get the balloon open takes a lot of pressure, but once it's blown up you can inflate and deflate rather easily - as long as you don't let the balloon fully collapse between breaths. If you let the balloon fully deflate, then it takes a hard breath to re-inflate.

Auto PEEP is like keeping the balloon slightly inflated at the end of expiration, making it easier to re-inflate with an inspiration.

Auto PEEP is a natural way to breath, and we do it automatically without anyone teaching you how to do it. Because it works. There is improved oxygenation and less work of breathing because you are keeping your alveoli open.

on tha money

I would just breath naturally.